Microbiological fouling has long been a problem with industrial aqueous systems. Aqueous industrial systems in which microbiological fouling can be a problem include industrial cooling water systems, in particular. However, microbiological fouling may be present and may cause problems in any aqueous containing system.
Microbiological fouling may result from the presence of any of a variety of organisms in an aqueous system. Among the organisms that are important in microbiological fouling are algae, fungi, and a variety of bacterial organisms. Such organisms may be introduced to aqueous industrial systems and intake water used in the system, from the environment, such as from the air or water, which could include, for example, an input of a component of foreign composition into the system or the introduction of contaminated equipment into a system.
Bacteria form a major component of microbiological fouling in aqueous systems. Bacteria can grow in almost any environment. Bacteria are loosely classified according to the environment in which they typically grow. Bacteria which are typically associated with microbiological fouling include anaerobic, facultative anaerobic, and aerobic bacteria. Anaerobic bacteria are particularly significant in microbiological fouling.
Among the problems associated with microbiological fouling are a loss of efficiency, corrosion of parts of aqueous systems, an increase in friction in water flowing through the system and a resulting decrease in efficiency and increase in required energy to move water through the system, as well as an increase in slime and inorganic deposition. An increase in material in the aqueous system can also decrease the efficiency of the system and clog the system by taking up volume within the system.
Once a fouling layer is detected and determined to be microbiological in nature, methods are used to control and eliminate the organisms responsible for the fouling. A variety of methods may be used to control microbial growth. Such methods may include changes to the conditions within the aqueous system and/or use of compounds having a microbiocidal effect.
According to one treatment protocol, the organisms causing microbiological fouling of aqueous systems are controlled using a variety of microbiocides. For instance, microbiocides such as chlorine or other known biocides may be injected into the system to control growth of microbiological organisms. The specific microbes requiring control affect the selection and method of application of the microbiocides used.
The addition of oxidizing biocides is routinely controlled through use of online oxidation-reduction potential (ORP) meters; however, this control is insensitive to potentially corrosive effects of high halogenation rates, which may be necessary to reach a target ORP range. Incorporating a corrosion rate signal would set an upper limit for halogenation (e.g., chlorination or bromination).